Study of characters and formation mechanism of hard crust on tidal flat of Yellow River estuary

The typical area was chosen on the tidal flat of the Yellow River estuary where hard crust develop,simulating wave load test with a light compactor was carried out to study the repeat liquefaction and change law of crust layer within one meter through the monitoring of pore water pressure and in-situ soil strength measure.The results revealed that the dynamic response varies a lot along depth and the strength of silt increases after repeat liquefaction;the upper crust layer increases more obviously than the down.The undisturbed samples were taken before and after vibrating;and quantitative analyzing of SEM structure images is carried out on the samples of different depths.The results revealed that some indexes of microstructure change evidently;such as asymmetry coefficient descended,granularity direction strengthed,granulometric fractal dimensions improved and figure coefficient improved and ratio of pore will descended etc.The transformation varied a lot along depth with the range mainly concentrated above the upper site.The relation between the dynamic response character and their microstructure changes has been discussed;and the character and formation mechanism of hard crust under the control law of microstructure are grasped primarily on this base.